Many optoelectronic devices used in fields such as optical communications involve changing the phase of an optical signal as a function of an external stimulus. The phase change can be the basis for the device functionality (e.g., Mach-Zehnder modulator, interferometric wavelength converter), or a residual effect such as chirp that is secondary to the device functionality (e.g., electroabsorption modulator). Such residual phase shift is important because of its potential impact on system performance. For the purposes of device design and system performance evaluation, it is important to be able to characterize the change in phase as a function of an external stimulus (optical phase transfer function).
Several methods are known for measuring the phase change of an optical signal as a function of an external stimulus. For example, the required information can be obtained indirectly from two separate measurements: the dependence of the intensity of the optical signal on the external stimulus, and the dependence of the alpha-parameter of the optical signal on the external stimulus (see for example Dorgeuille et al., IEEE J. Quantum Electron., 30:2565–2572, 1994). Alternatively, a balanced lock-in detection technique can be used to measure the amplitude and phase of the interference generated by two ultra short optical pulses (signal from the device under test and the reference signal), as described in Romstad et al., IEEE Photon. Technol. Lett., 14:621–623, 2002. In another technique, a box car averager is used to measure the amplitude and phase of interference signals generated by a bulk optic interferometer with a moving mirror (Yu, J., “The Beam Propagation Method and Its Application to the Design of Semiconductor Modulators,” Ph.D. thesis, Queen's University at Kingston, Kingston, Ontario, 1994). Lastly, an interferometer can be used to convert changes in the optical phase to changes in power (see Yoshida et al., Electronics Letters, 30:1795–1796, 1994).
However, such known techniques have limitations including (1) the result of interest is obtained indirectly, (2) the measurement setup is complicated, and (3) the measurement setup uses specialized and expensive equipment that may not necessarily be readily available.